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Eye Shutter

Frequently people land on this site with search queries like "what part of the eye corresponds to the camera shutter". With a camera, the shutter opens for a very precise amount of time and allows light to hit the film or sensor inside the camera. The closest comparison to that in the eye would be the eyelid that can open and close but its purpose is more analogous to that of the lens cap than the shutter. Shutter mechanisms come in a variety of configurations. More detailed information about camera shutters can be found in this article [Wikipedia].

Camera lenses also have a diaphragm iris [Wikipedia] which adjusts to increase or decrease the amount of the available light that can pass through it during any given period of time. This corresponds directly to the iris in the eye [Wikipedia] which serves the same purpose. I suspect many people confuse this with the diaphragm-type shutter mechanism, however both the eye's iris and that of the camera are visible through the lens while the shutter is generally inside the camera and out of sight. In modern cameras, the iris is usually fully open except at the moment when a picture is taken so it can be seen to move right about the same time as the shutter.